golang提供內建函數cap用於查看channel緩沖區長度。
cap的定義如下：
func cap(v Type) int
The cap built-in function returns the capacity of v, according to its type:
- Array: the number of elements in v (same as len(v)).等同於len
- Pointer to array: the number of elements in *v (same as len(v)).等同於len
- Slice: the maximum length the slice can reach when resliced;
if v is nil, cap(v) is zero.對於slice，表示在不重新分配空間的情況下，可以達到的切片的最大長度。如果切片是nil， 則長度為0.
- Channel: the channel buffer capacity, in units of elements;表示緩沖區的長度。
if v is nil, cap(v) is zero. 如果通道是nil，則緩沖區長度為0。
Example
package main
import ("fmt")
func main(){
ch1 := make(chan int)
ch2 := make(chan int, 2)//緩沖區長度為2
fmt.Println("ch1 buffer len:", cap(ch1))
fmt.Println("ch2 buffer len:", cap(ch2))
}
output:
ch1 buffer len:0
ch2 buffer len:2